1. Section 14.1 Summary – pages 369-379
Early History of Earth
What was early Earth like? probably very hot.
Volcanoes might have frequently spewed lava and gases, these gases helped form Earth’s early atmosphere.
About 4.4 billion years ago, Earth might have cooled enough for the water in its atmosphere to condense.
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2. Section 14.1 Summary – pages 369-379
History in Rocks and fossils
The oldest rocks that have been found on Earth formed about 3.9 billion years ago.
About 95 percent of the species that have existed are extinct.
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3. Section 14.1 Summary – pages 369-379
Fossils-Clues to the past
Types of Fossils
A fossil is evidence of an organism that lived long ago that is preserved in Earth’s rocks.
Fossils Types
Formation
A trace fossil is any indirect evidence
A trace fossil is any indirect evidence
Trace fossils
left by an animal and may include a
footprint, a trail, or a burrow.
When minerals in rocks fill a space
Casts
left by a decayed organism, they make
a replica, or cast, of the organism.
A mold forms when an organism is
A mold forms when an organism is
Molds
buried in sediment and then decays,
leaving an empty space.
Petrified/
Petrified-minerals sometimes penetrate
and replace the hard parts of an
Permineralized
organism. Permineralized-void spaces
fossils
in original organism infilled by
minerals.
Amber-
At times, an entire organism was
Preserved or
quickly trapped in ice or tree sap that
frozen fossils
hardened into amber.
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4. Section 14.1 Summary – pages 369-379
Paleontologists
Paleontologists, scientists who study ancient fossils
determine the kinds of organisms that lived during the past
gain knowledge about ancient climate and geography.
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5. Fossil formation
For fossils to form, organisms usually have to be buried in mud, sand, or clay soon after they die.
Most fossils are found in sedimentary rocks. These rocks form at relatively low temperatures and pressures that may prevent damage to the organism.

6. Section 14.1 Summary – pages 369-379
The Fossilization Process
A Protoceratops drinking at a river falls into the water and drowns
Sediments from upstream rapidly cover the body, slowing its decomposition. Minerals from the sediments seep into the body.
Over time, additional layers of sediment compress the sediments around the body, forming rock. Minerals eventually replace all the body’s bone material.
Earth movements or erosion may expose the fossil millions of years after it formed.
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Relative dating
One method is a technique called relative dating.
If the rock layers have not been disturbed, the layers at the surface must be younger than the deeper layers.
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Radiometric dating
To find the specific ages of rocks, scientists use radiometric dating techniques utilizing the radioactive isotopes in rocks.
radioactive isotopes are atoms with unstable nuclei that break down over time, giving off radiation.
scientists use the rate of decay as a type of clock - called its half-life.
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9. Section 14.1 Summary – pages 369-379
Radiometric dating
potassium-40, a radioactive isotope that decays to argon-40, to date rocks containing potassium bearing minerals. Chemists have determined that potassium-40 decays to half its original amount in 1.3 billion years.
Scientists use carbon-14 to date fossils less than years old. Carbon-14 decays to half its original amount in 5730 years.
Errors can occur if the rock has been heated, causing some of the radioactive isotopes to be lost or gained.
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10. Section 14.1 Summary – pages 369-379
A Trip Through Geologic Time
scientists have put together a geologic time scale, or calendar, of Earth’s history.
the geologic time scale is divided into four sections,
the Precambrian Era,
the Paleozoic Era,
the Mesozoic Era,
and the Cenozoic Era.
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11. Section 14.1 Summary – pages 369-379
The geologic time scale
The divisions are distinguished by the organisms that lived during that time interval.
The fossil record indicates that there were several episodes of mass extinction that fall between time divisions.
The geologic time scale begins with the formation of Earth about 4.6 billion years ago.
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12. Section 14.1 Summary – pages 369-379
Precambrian
The oldest fossils are found in Precambrian rocks that are about 3.4 billion years old.
The fossils resemble the forms of modern blue-green algae.
The Precambrian accounts for about 87 percent of Earth’s history.
Beginning of the Precambrian = unicellular prokaryotes appear to have been the only life forms on Earth.
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13. Section 14.1 Summary – pages 369-379
Precambrian
About 1.8 billion years ago, the fossil record shows that more complex eukaryotic organisms, living things with membrane-bound nuclei in their cells, appeared.
Major Life Form
Prokaryotes
Invertebrates
Life evolves
Eukaryotes
Major Events
Period Era
Precambrian
Million Years Ago
4000
3500
1800
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14. Section 14.1 Summary – pages 369-379
Precambrian
By the end of the Precambrian, about 543 million years ago, multicellular eukaryotes, such as sponges and jelly-fishes, diversified and filled the oceans.
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Paleozoic
In the Paleozoic Era, which lasted until 248 million years ago, many more types of animals and plants were present on Earth.
oceans had many types of animals, including worms, sea stars, and unusual arthropods.
During the first half of the Paleozoic, fishes, the oldest animals with backbones
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16. Diversity during Paleozoic
During the last half of the era, the fossil record shows that reptiles appeared and began to flourish on land.
First vertebrates
First land plants
First jawed fishes
First amphibians
Conifers dominant
First seed plants
First reptiles
Cambrian
Ordovician
Silurian
Devonian
Carboniferous
Permian
Paleozoic Era
543
491
443
417
354
323
290
Million Years Ago

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Mesozoic
The Mesozoic Era began about 248 million years ago.
Fossils show that mammals appeared on Earth at this time.
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Mesozoic
These fossils of mammals indicate that early mammals were small and mouse-like.
The middle of the Mesozoic, called the Jurassic Period, began about 206 million years ago.
First flowering plants
Flowering plants dominant
First dinosaurs
First mammals
First birds
Period
Triassic
Jurassic
Cretaceous
Era
Mesozoic Era
Million Years Ago
248
206
144
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Changes during Mesozoic
The theory of continental drift, suggests that Earth’s continents have moved during Earth’s history and are still moving today at a rate of about six centimeters per year.
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20. Section 14.1 Summary – pages 369-379
Changes during the Mesozoic
Click image to view movie.
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Changes during the Mesozoic
Early in the Mesozoic, the continents were merged into one large landmass. During the era, this super-continent broke up and the pieces drifted apart.
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22. Changes during the Mesozoic
The theory for how the continents move is called plate tectonics.
According to this idea, Earth’s surface consists of several rigid plates that drift on top of a plastic, partially molten layer of rock.
These plates are continually moving-spreading apart, sliding by, or pushing against each other. The movements affect organisms.

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The Cenozoic Era
The Cenozoic began about 65 million years ago.
It is the era in which you now live. Mammals began to flourish during the early part of this era.
Primates first appeared approximately 75 million years ago and have diversified greatly.
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The Cenozoic Era
The modern human species appeared perhaps as recently as 200,000 years ago.
Mammals
dominant
Humans
evolve
Tertiary
Quaternary
Period Era
Cenozoic Era
Million Years Ago 65
1.8
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